26-12-2017, 02:19 PM
Hi All
I haven't posted for quite a while just other things had to take priority.
I have been dipping in and out of this project any chance I got, hopefully this post will bring it somewhat up to date.
The video decoder defaults to NTSC at start up if no signal present at its input. As I am using a Frame sync pulse that is derived from the field indicator signal this causes a problem as the frame sync pulse resets the 405 sync generator and when it arrives at 30 Hz instead of the expected 25 Hz it really messes up the syncs and the test card don't display as it should.
There are probably signals from the decoder that indicate when a PAL signal is present but instead I decided to detect PAL by count the lines in each frame and when PAL is not present the Frame pulse is disabled allowing the 405 sync generator to free run.
I have populated the RF modulators and they are working OK. All 13 channels appear to be working good except for the sound on Channel 13. There is a continuous steady tone on it of maybe 200 or 300 HZ.
It is there even when the Video modulator is disabled or when the audio input is grounded.
Viewing the Sound RF on the scope there is no visible AM modulation and when tuned into the center the tone is at lowest, tuning either side of center increases the volume of the tone a lot. This makes me think it must me some form of FM modulation.
I have started to finalize the PCB but before I could do this I needed to chose a case for it. The maximum size of the PCB I limited to 100mm X 100mm as once over this size the cost off manufacture increases dramatically. I would like to mount all the components including the switches and connectors on the PCB. They wont all fit along one edge of the PCB so will have to used two edges, because of this the distance between the front and back panels of the case will need to be 100mm or less and to facilitate fitting the PCB into the case the case will have to have removable front and rear panels. Another criteria is the FPGA development board will need to fit between the PCB mounting posts of the case.
I found one that suits the bill it is made by multicomp part No. MCRM2015M, it will allow a PCB size of 100mm X 89mm which is large enough to to have everything PCB mounted. On the back panel will be 3 X phono sockets for audio and video, a power socked and a F connector for RF out. The front panel will have 3 X 3 position and 3 X 2 position toggle switches for options, a hex switch for Chanel selection, a LED and a phono socket for video out.
Frank
I haven't posted for quite a while just other things had to take priority.
I have been dipping in and out of this project any chance I got, hopefully this post will bring it somewhat up to date.
The video decoder defaults to NTSC at start up if no signal present at its input. As I am using a Frame sync pulse that is derived from the field indicator signal this causes a problem as the frame sync pulse resets the 405 sync generator and when it arrives at 30 Hz instead of the expected 25 Hz it really messes up the syncs and the test card don't display as it should.
There are probably signals from the decoder that indicate when a PAL signal is present but instead I decided to detect PAL by count the lines in each frame and when PAL is not present the Frame pulse is disabled allowing the 405 sync generator to free run.
I have populated the RF modulators and they are working OK. All 13 channels appear to be working good except for the sound on Channel 13. There is a continuous steady tone on it of maybe 200 or 300 HZ.
It is there even when the Video modulator is disabled or when the audio input is grounded.
Viewing the Sound RF on the scope there is no visible AM modulation and when tuned into the center the tone is at lowest, tuning either side of center increases the volume of the tone a lot. This makes me think it must me some form of FM modulation.
I have started to finalize the PCB but before I could do this I needed to chose a case for it. The maximum size of the PCB I limited to 100mm X 100mm as once over this size the cost off manufacture increases dramatically. I would like to mount all the components including the switches and connectors on the PCB. They wont all fit along one edge of the PCB so will have to used two edges, because of this the distance between the front and back panels of the case will need to be 100mm or less and to facilitate fitting the PCB into the case the case will have to have removable front and rear panels. Another criteria is the FPGA development board will need to fit between the PCB mounting posts of the case.
I found one that suits the bill it is made by multicomp part No. MCRM2015M, it will allow a PCB size of 100mm X 89mm which is large enough to to have everything PCB mounted. On the back panel will be 3 X phono sockets for audio and video, a power socked and a F connector for RF out. The front panel will have 3 X 3 position and 3 X 2 position toggle switches for options, a hex switch for Chanel selection, a LED and a phono socket for video out.
Frank
